Particle model
You can use the idea of particles to explain the properties of solids, liquids and
gases. The strength of bonds between particles is different in all three states. It
explains why solids cannot flow, and why gases can be compressed.
Solids
Steel, plastic and wood are solids at room temperature. Ice is solid water.
The particles in a solid have the following characteristics:

they are close together

they are arranged in a regular pattern

they are held together by strong forces called bonds

they can vibrate in a fixed position

they cannot move from place to place
The table shows some of the properties of solids and why they are like this.
Property of solids
Why they are like this
They have a fixed shape and cannot flow.
The particles cannot move from place to place.
They cannot be compressed or squashed.
The particles are close together and have no space to move into.
Liquids
Mercury, lemonade and water are liquids at room temperature.
The particles in a liquid are:

close together

arranged in a random way
The particles in a liquid can:

move around each other
The bonds in a liquid are strong enough to keep the particles close together, but weak
enough to let them move around each other.
The table shows some of the properties of liquids and why they are like this.
Property of liquids
Why they are like this
They flow and take the shape of their container.
The particles can move around each other.
They cannot be compressed or squashed.
The particles are close together and have no space to move into.
Gases
Air, helium and chlorine are gases at room temperature. Water vapour is water as a gas.
The particles in a gas are:

far apart

arranged in a random way
The particles in a gas can:

move quickly in all directions
There are no bonds between the particles in a gas, so they are free to move in any direction.
The table shows some of the properties of gases and why they are like this.
Property of gases
Why they are like this
They flow and completely fill their container.
The particles can move quickly in all directions.
They can be compressed or squashed.
The particles are far apart and have space to move into.
Flowing
Liquids and gases do not have a fixed shape. They can flow and fill their containers, but solids
cannot. The particle model explains why.
Solids
Solids cannot flow because their particles are only able to vibrate and cannot move from
place to place.
Liquids
Liquids can flow because their particles can move over each other. When water is poured into
a glass, the particles of water move over each other and into the corners of the glass. The
particles keep on moving over each other as the water takes the shape of the glass. The
animation shows how this works.
Gases
Gases can flow because their particles can move in all directions. When a Bunsen burner is
connected to a gas tap and turned on, natural gas flows through the rubber tubing. The
particles of natural gas are free to move anywhere inside the tubing, and pressure forces
them through the tubing into the Bunsen burner.
Arrangement and movement
The table summarizes the arrangement and movement of the particles in solids, liquids and
gases. It also shows simple diagrams of the arrangement of the particles that you should be
able to draw and recognize.
Arrangement of particles
Movement of particles
Diagram
Solid
Liquid
Gas
Close together
Close together
Far apart
Regular pattern
Random arrangement
Random arrangement
Vibrate on the spot
Move around each other
Move quickly in all directions